mysql - 如何从 rake 任务建立连接？

Question

我需要创建一个 rake 任务，从 MySQL 数据库中获取表行，解析数据，然后插入到 Oracle 数据库中。数据库位于两个不同的主机上。

我目前的尝试:

namespace :import_from_mysql do
  class MySQLConnection < ActiveRecord::Base
    self.abstract_class = true
    establish_connection({
    :adapter  => 'mysql',
    :host     => 'xxx.xxx.com',
    :database => 'sample_database',
    :username => 'username',
    :password => 'password'
    })
  end

  class MySQLTable < MySQLConnection
    self.table_name = "users"
    self.primary_key = "id"
    self.inheritance_column = "something_unique_here"
  end

  desc "Parse data before inserting to oracle database"
  task :insert_to_oracle => :environment do |t|
    puts "Rake task has begun...\n\n"
    puts "Parsing data from MYSQL...\n\n"

    MySQLTable.establish_connection

    puts "Rake task has completed!"
  end
end

但是 MySQLTable.establish_connection 建立了到我的本地数据库的连接，即使我正在尝试连接到 mysql_adapter 也是如此。

当我尝试使用以下命令建立连接时，我能够连接到 MySQL 适配器，但我不知道在建立连接后如何访问我的表:

ActiveRecord::Base.establish_connection({:adapter => "mysql", :database => "sample_database", :host => "xxx.xxx.com", :username => "username", :password => "password" })

知道为什么它一直连接到 sqlite 吗？而在成功建立与mysql的连接后，如何在MySQLTable.establish_connection语句之后选择表行？

Answer 1

通过使用 ActiveRecord::Base 生成的连接，您可以对连接到的任何数据库执行 SQL 语句。像这样:

connection = ActiveRecord::Base.establish_connection(
  :adapter  => "mysql",
  :host     => "faraway",
  :username => "myuser",
  :password => "mypass",
  :database => "somedatabase"
)
connection.execute('SELECT * FROM users')

一旦建立，连接也可以从 ActiveRecord::Base 类中引用。

ActiveRecord::Base.establish_connection(...)
ActiveRecord::Base.connection.execute(...)